RE: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[Dexuan Cui <decui@microsoft.com>]

> -----Original Message-----
> From: devel [mailto:driverdev-devel-bounces@linuxdriverproject.org] On
> Behalf Of K. Y. Srinivasan
> Sent: Tuesday, April 28, 2015 9:15
> To: davem@davemloft.net; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; devel@linuxdriverproject.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com
> Subject: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()
> 
> Commit commit b08cc79155fc26d0d112b1470d1ece5034651a4b
> eliminated memory
> allocation in the packet send path. This commit introduced a bug since it
> did not account for the case if the skb was cloned. Fix this bug by
> using the pre-reserved head room only if the skb is not cloned.
> 
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> ---
>  drivers/net/hyperv/netvsc_drv.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/hyperv/netvsc_drv.c
> b/drivers/net/hyperv/netvsc_drv.c
> index a3a9d38..7eb0251 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -421,7 +421,7 @@ check_size:
> 
>  	pkt_sz = sizeof(struct hv_netvsc_packet) + RNDIS_AND_PPI_SIZE;
> 
> -	if (head_room < pkt_sz) {
> +	if (skb->cloned ||  head_room < pkt_sz) {
>  		packet = kmalloc(pkt_sz, GFP_ATOMIC);
>  		if (!packet) {
>  			/* out of memory, drop packet */
> --

Without the patch, the guest can panic due to memory corruption.

I confirm the patch can fix the panic I saw.

Tested-by: Dexuan Cui <decui@microsoft.com>

Thanks,
-- Dexuan